Known in the past has been an internal combustion engine provided in an exhaust passage with a filter for trapping particulate matter (PM) contained in exhaust gas so as to purify exhaust gas discharged from the combustion chambers. In such an internal combustion engine, fuel is made to oxidatively react in a catalyst provided at an upstream side of the filter, and the heat of reaction caused by the oxidation reaction is used to burn off the PM deposited on the filter as “processing for filter regeneration”.
However, processing for filter regeneration can be performed when the internal combustion engine is in a predetermined operating state. For this reason, in the internal combustion engine described in PLT 1, in order to prevent the filter from being clogged by the PM while processing for filter regeneration cannot be performed, a liquid substance such as condensation water is fed to the PM on the filter.